Utilizing the highly correlated quantum NOON states of particles, we have implemented a proof-of-principle quantum thermometer using the NMR technique for measuring the variation of local magnetic field with the temperature variation. The system used was the star-topology system of hexafluorophosphate molecules and the thermometer showed a sensitivity of
85nT/oC. Using the hexafluorophosphate and the trimethylphosphite spin systems, we have quantified the advantage of the quantum protocol over the classical one for measuring magnetic field. The quantum protocol showed the best performance for a time evolution in the quantum circuit of
T=20ms, where the errors in the measurement scaled as the Heisenberg limit
1/N.
We describe a method for quantitative characterization of radio-frequency (RF) inhomogeneity using NOON states. NOON states are special multiple-quantum coherences which can be easily prepared in star-topology spin-systems. In this method we exploit the high sensitivity of the NOON states for z-rotations. As a result, Torrey oscillations with NOON states decay much faster than that of single quantum coherences. Therefore the present method requires shorter pulse durations, and enables the study of inhomogeneity at higher RF powers. To model such a inhomogeneity profile, we propose a two-parameter asymmetric Lorentzian function. The experiments are carried out in 1H channels of two different high-resolution NMR probes and the results are compared. Finally, we also extend the NOON state method to characterize the inhomogeneity correlations between two RF channels. We obtain the correlation profile between 1H and 31P channels of an NMR probe by constructing a five-parameter asymmetric-3D Lorentzian model.
Path-entangled N-photon systems described by NOON states are the main ingredient of many quantum information and quantum imaging protocols. Our analysis aims to lead the way toward the implementation of both NOON-state sources and their applications. To this end, we study the functionality of "real" NOON-state sources by quantifying the effect real experimental apparatuses have on the actual generation of the desired NOON state. In particular, since the conditional generation of NOON states strongly relies on photon counters, we evaluate the dependence of both the reliability and the signal-to-noise ratio of "real" NOON-state sources on detection losses. We find a surprising result: NOON-state sources relying on nondetection are much more reliable than NOON-state sources relying on single-photon detection. Also the comparison of the resources required to implement these two protocols comes out to be in favor of NOON-state sources based on nondetection. A scheme to improve the performances of "real" NOON-state sources based on single-photon detection is also proposed and analyzed.